Hi Shawn and welcome back to the Disney Parks Moms Panel!
It sounds like your sister is planning for culinary adventure by taking advantage of the
Deluxe Dining Plan. It's so convenient to have your meal costs taken care of before your vacation begins. Your sister also sounds generous in wanting to use her some of her Dining Entitlements to take your parents out for a meal.
I hope she will be pleased to hear that she is more than welcome to use her credits to pay for your parents' meal. When they are seated at a restaurant, their server will ask if anyone is using a Disney Dining Plan. Your sister will simply need to tell the server how many people in their party will be using the Dining Plan and that she is planning to use her entitlements. For more information, my friend Diane had a great answer about her
experience with sharing Dining Entitlements. Shawn, thank you for coming back to ask another great question. You are kind to be helping your sister with her plans. Generosity must run in your family! Be sure to let us know if we can help you or your sister with any other questions!
Wishing you a magical day,
Amy H.